The importance of regional blood flow in tumor and normal tissue cannot be understated when considering localized hyperthermia therapy. Hyperthermia is fast becoming an important modality in the treatment of cancer and the physical parameters governing the deposition of energy in biological tissues are taking on great significance. Initial data from this laboratory indicate that regional blood flow in both tumor and normal tissue is a dynamic parameter which changes throughout treatment intervals. If differences exist between tumor and normal tissue blood flow and their response to hyperthermia challenge, regions of poor vascularity and subsequent compromised blood flow may be more susceptible to hyperthermia treatment. Initial blood flow data suggests that differences exist between tumor and normal tissue, and this observation may render tumors more susceptible to hyperthermia damage than normal tissue counterparts if treatment times are planned appropriately. It, therefore, becomes important to measure blood flow in both tumor and normal tissue and to quantitate the relationships between regional temperature increases and tissue vascularity. This investigation will measure blood flow in the normal tissue of mongrel dogs as a function of treatment time and fractionation scheme. These blood flow determinations will be made for different treatment temperatures and specific fractionation intervals through the use of radioactively labeled microspheres. The information obtained from radioactive microspheres will be employed with various solutions of the bio heat transfer equation to attempt to generate accurate models of regional tissue blood flow from tissue temperature analysis (thermal clearance, etc.). Once the validity of the mathematical model is confirmed for a variety of treatment temperatures, blood flow analysis will be conducted in a series of both healthy and tumor-bearing animals. The network for accessing tumor-bearing animals for hyperthermia treatment has been established at the Medical College of Ohio for approximately two years, and this referral network is presently well established. Employing these tumor-bearing animals, blood flow determinations in a variety of tumors can be performed, and with the aid of various mathematical models, optimum treatment times and fractionation schemes will be predicted.